As an antivibration device for supporting and fixing a vibration generator such as an automotive engine or transmission so as not to transmit vibrations thereof to a vehicle body frame, hydraulic style antivibration devices are known.
Hydraulic antivibration devices each have a liquid-sealed chamber comparted by partition means into a first and a second liquid chambers, which are put in communication with each other through an orifice, and perform both a vibration attenuating function and a vibration insulating function due to a fluid fluidization effect through the orifice between the first and second liquid chambers and a vibration-deadening effect of a vibration-isolating base.
Of these, there is such a hydraulic antivibration device that the partition means comprises an elastic partition membrane made of rubber-like elastomer material and a pair of displacement-regulating members regulating the displacement amount of the elastic partition membrane from both sides thereof.
According to the hydraulic antivibration device of this type, when a relatively small amplitude vibration is input, the elastic partition membrane is subjected to reciprocating displacement, thereby absorbing a hydraulic pressure fluctuation between both liquid chambers, so that a low dynamic spring characteristic can be obtained. On the other hand, when a relatively large amplitude vibration is input, for example, owing to irregularities of the travelling road surface, the displacement-regulating members serve to regulate the displacement amount of the elastic partition membrane from its both sides to enhance the membrane stiffness, thereby rendering the fluid easy to fluidize between both liquid chambers through the orifice, so that a high damping characteristic can be obtained.
However, a problem with the hydraulic antivibration device of this type was that because of the construction that the elastic partition membrane is made to impinge (abut) on the displacement-regulating members, the displacement-regulating members oscillate upon impinging, which oscillation is transmitted to the body frame to generate a strange sound (noise).
As a technology of suppressing the generation of such strange sounds, for example, WO 02/095259 A1 discloses, in connection with a hydraulic antivibration device constructed so that a vibration-isolating base made of rubber-like elastomer material is interconnected between a boss member and a cylindrical main body member and a liquid-filled chamber is formed between a diaphragm provided at the main body member and a vibration-isolating base, a technology for connecting the boss member to a body frame side while connecting the main body member to an engine side (Patent Reference 1).
According to this technology, it is possible to construct a part of a vibration transmission path from partition means (the elastic partition membrane and the displacement-regulating members) to the vehicle body frame by the vibration-isolating base, and consequently, even if the elastic partition membrane impinges on the displacement-regulating members, which in turn oscillate, it is possible to suppress transmission of the oscillation to the body frame by virtue of the vibration insulating effect of the vibration-isolating base constituting a part of the vibration transmission path, thus reducing the generation of strange noises.
[Patent Reference 1] WO 02/095259A1 (FIGS. 1, 2, etc.)